Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Materials Science and Engineering


G.C. Weatherly


G. Purdy


This work has involved a study of diffusion and ion implantation enhanced diffusion in GaAs based semiconductor heterostructures. A knowledge of kinetic parameters underlying the diffusion process is of practical value in the fabrication of optoelectronic devices. Two main problems have been explored. (a) Thermal interdiffusion of (InGaAs/GaAs)quantum well structures and superlattices. Transmission electron microscopy, X-ray diffraction and photoluminescence experiments have been undertaken to follow the temporal evolution of the indium composition during annealing of the superlattice. A linear model of diffusion has been utilized to calculate the evolution of strain, indium composition and the X-ray diffraction intensity during annealing. Calculation of energy levels of the electrons and holes in the superlattice structure and their evolution with annealing have also been performed following a transfer matrix approach. This has been used to predict the experimentally observed trends in photoluminescence. Non linear aspects of diffusion including composition dependence and strain dependence (by growth on 311A substrates) have also been experimentally examined. (b) Ion implantation enhanced disordering of III-V compound semiconductor heterostructures (InGaAs/GaAs, GaAs/AlGaAs). Various parameters which influence the disordering process, namely the implant energy, ion species, implant temperature and heterostructure composition have been studied with transmission electron microscopy (conventional/high resolution) and photoluminescence techniques. Several interesting phenomena with respect to the position and crystallographic nature of implant damage have been observed. A phenomenological model to rationalize data has been developed by numerically solving the governing diffusion equations.

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